Several studies have reported declining student enrolment rates in optional physical education. This study--incorporating constructs from social cognitive, self-determination, and body image theory--investigated factors that might be influential to this trend. Surveys were administered to 227 tenth-grade students from five schools in one school district of Ontario, Canada. MANOVA results revealed a significant main effect difference in variables by gender and enrollment group but not by the interaction. Enrollees had statistically higher motivation (domain value, self-efficacy, perceived autonomy support, and autonomous regulation), PE grade, and weekly levels of exercise beyond physical education. Qualitatively, nonenrollees reported more social concerns, less domain value, and disliked activities like fitness training, health content, and competition. Females had statistically higher body size discrepancy and qualitatively more domain value and concern about the social setting and the type of activities. Implications for the retention of high school physical education students are discussed. (Contains 4 tables.)